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Characterization of Planetary Atmospheres

Molaverdikhani, Karan

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Abstract

After the discovery of the first exoplanet in 1990’s and a fast growing number of discoveries since then, there have been many attempts to observe and characterize their atmospheres. In particular, water and methane have been the focus of many investigations due to their relevance to the origin of life and habitability, as well as their major roles to shape the structure of planetary atmospheres. Abundances retrieved for these species can be also used as a tracer of carbon-to-oxygen ratio (C/O) and metallicity of these atmospheres; hence potentially linking the formation scenarios with the observations. Water’s spectral signature is everywhere, but despite many efforts, there has been only one robust detection of methane and only recently. The question is, “where is methane?”. By applying a hierarchical modelling approach (utilising more than 177,000 thermochemical equilibrium cloud-free, disequilibrium cloud-free, and thermochemical equilibrium cloudy models) we predict that there are four classes of irradiated gaseous planets; two of them (Class-I and Class-II; Teff<1650 K) likely to show signatures of CH4 in their transmission spectra, if cloudy-free and C/O above a certain threshold (aka the “Methane Valley”). The effect of disequilibrium processes on the classification found to be modest with a more continuous transition between Class-II and III planets. Clouds, however, heat-up the deeper parts of Class-I and Class-II planets; removing CH4 from the photosphere. Simultaneously, clouds obscure any molecular features; hence making the observation of methane even more challenging.

Item Type: Dissertation
Supervisor: Henning, Prof. Dr. Thomas
Place of Publication: Heidelberg
Date of thesis defense: 5 February 2020
Date Deposited: 21 Feb 2020 12:28
Date: 2020
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 520 Astronomy and allied sciences
530 Physics
540 Chemistry and allied sciences
Uncontrolled Keywords: Exoplanets, Atmospheres, Chemical Kinetic Modeling
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